IMO, even with very high loads these parachutes should not have separated

Every parachute has a maximum load that it can withstand. If the Orion chutes were designed to open at a speed of say 350 MPH and the test capsule was going much faster, something is going to give. Since the test rig parachutes failed to orient the capsule properly and establish the proper speed, everything went downhill from there (literally).

The drogue chutes failed (probably going too fast), so the test article began to tumble. When the pilot chutes tried to open the mains, they weren't able to get the mains open. It's hard to tell but it appears the main chute lines were tangled. That happens a lot when you try to open a chute while tumbling.